1. Field of the Invention
This invention relates to a functional vacuum microelectronic device.
2. Description of the Prior Art
Recently, with growing development of the fine processing technique, the research and the study for the vacuum microelectronic filed-emission devices (VMFE), namely, the cold cathode devices, have become active. Some types of them are studied well because they have various advantageous effects. In the functional vacuum microelectronic field-emission devices, electron emission is carried out by a strong electric field of about 10.sup.7 V developed by concentrating electric lines of force at a tip of an emitter which is processed to have a needle shape such that a curvature of the tip of the emitter is less than hundreds nanometers in order to emit electrons. The tip of the emitter is formed in the vertical direction with respect to the substrate.
As a new device using the above-mentioned microelectronic field-emission device, a vacuum transistor of the field-emission type disclosed in IEDM 86, 33.1, p776 is proposed. Its structure will be described with reference to drawings. FIG. 24 is a cross-sectional view of a prior art field-emission type vacuum transistor.
In FIG. 24, silicon Si is used for a substrate 200. A conical emitter 201 as an electron emitting portion which is formed by processing the substrate 200. On the substrate 200, an insulation layer 202 made of SiO.sub.2 is formed around the emitter 201. A gate 203 and a collector 204 are formed on the insulation layer 202 at a given intervals. A bias power supply 206 and a signal input portion 205 connected in series are connected between the emitter 200 and the gate 203. A load resistor 207 and a collector power supply 208 connected in series are connected between the emitter 201 and the collector 204.
In the above-mentioned structure, when a suitable bias potential is applied between the gate 203 and the emitter 201 by the bias power supply 206 and a voltage of the signal input portion 205 is changed, electrons 211 can be emitted from the emitter 201 in accordance with a sum voltage of the bias voltage and an input signal voltage, i.e., a voltage between the gate 203 and the emitter 201. In this state, electrons 211 emitted into a vacuum space can be taken into the collector 204 by application of a sufficient voltage by the collector power supply 208. As the result, a current flows in the resistor 207, so that a voltage between the terminals 209 and 210 will change. That is, a voltage of an output terminal 210 of the collector 204 can be changed in accordance with the voltage change of the signal input portion 205. That is, some type of transistor operation or switching operation is achieved. Moreover, in this vacuum microelectronic field-emission device, a high speed operation is possible because electrons runs through a vacuum space as against that electrons run through a solid material in the transistor.
However, in the above-mentioned prior art, a semiconductor material is used for the emitter and processing of the emitter 201 is carried out by anisotropic etching using a unique characteristic of its material. As mentioned, because the material of the emitter 201 is a semiconductor, a work function become higher than that of the metal material, so that a quantity of electron emission becomes small. Accordingly, a signal output level become small, so that there is a problem that its characteristic cannot be utilized sufficiently as a switching device, etc.
Moreover, there is proposed a new device using the above-mentioned small vacuum microelectronic field-emission device is proposed as a three-terminal device shown in FIG. 25, disclosed in the papers of lecture of No. 51 meeting of The Japan Society of Applied Physics, 1990, p1209. FIG. 25 is a plan view of the three-terminal device of a prior art and FIG. 26 shows a cross section taken on line K--K shown in FIG. 25. Hereinbelow will be described its structure with reference to FIGS. 25 and 26. The three-terminal device has, on a substrate 251, a sawtooth-shaped emitter 252, a gate 253 formed a given interval apart from a tip of the emitter 252 and the gate portion is formed in a cylindrical-shape, and an anode 254 formed a given interval apart from the gate 253 on the opposite side of the gate 253 from the emitter 252. Grooves are made by removing portions of the substrate 251 between the emitter 252 and the gate 253, and between the gate 253 and the anode 254.
The production method of the three-terminal device will be described with reference to FIGS. 27A to 27E. As shown in FIG. 27A, a tungsten (W) film 262 is formed on a substrate 261. Then, a resist is formed in a given shape on the tungsten film 262. Then, as shown in FIG. 27B, the tungsten film 262 is etched using the resist 263 as a mask. Then, as shown in FIG. 27C, a resist 265 is formed again in a given shape to form portions of the gate 264 into a cylindrical shape. After this, as shown in FIG. 27D, the tungsten film 262 is etched again. As mentioned above, the emitter 266, gate 264, and an anode 267 are formed. Finally, as shown in FIG. 27E, portions of the substrate are removed by etching to form the grooves.
Hereinbelow will be described operation of the three-terminal device having the above-mentioned structure. In FIG. 25, electrons are emitted from the emitter 252 when a voltage is applied between the emitter 252 and the gate 253 such that a potential of the emitter 252 is negative and a potential of the gate 253 is positive and an electric field whose intensity is higher than a given value. The amount of emitted electrons can be changed by variation of the applied voltage. The electrons emitted from the emitter 252 can be taken into the anode 254 by applying a sufficient voltage to the anode 254. That is, the amount of electrons flowing into the anode can be changed by variation of a voltage between the emitter 252 and the gate 253. Therefore, a kind of transistor or switching operation is achieved. Moreover, in this vacuum microelectronic field-emission device, a high speed operation is possible because electrons run through a vacuum space as against that electrons run through a solid material in the transistor.
However, in the above-mentioned prior art structure, positioning is necessary because resist-patterning is carried out twice in the production method. Therefore, because a fine processing technique is required, there is a problem in reproducibility and stability of characteristics of the device.